Induction-motor control.



E. F. W. ALEXANDERSON! INDUCTION MOTOR GONTROL.

APPLICATION FILED JULY 12, 1906.

' Patented Oct. 20, 1908.

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INDUCTION MOTOR CONTROL.

APPLICATION FILED JULY 12, 1906.

Patented 0011.20, 1908.

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E. F. W. ALEXANDERSON. INDUCTION MOTOR CONTROL.

APPLIUATION FILED JULY 12, 1906.

901,513. Patented 0ct.20,1908.

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ERNST F. W. ALEXANDERSON, or scnRNEc'rAnY, NEW roan, ASSIGNOR 'ro GENERAL ""ELEGTRIO COMPANY, -A CORPORATION OF'NEW YORK. I

INDUCTION-MOTOR CONTROL.

Specification of Letters Patent.

Patented Oct. 20, 1908.

Application filed July 12, 1906- Serial No. 325,844.

tady, State of New York, have invented certain new and useful Im rovements in Induction-Motor Control, 0 which the follow i is a specification.

Iy invention relates to the control of in-- duction motors, and is articularly applicable to the control of sing -phase locomotives driven by induction motors.

It has been proposed heretofore in the case of loads driven from a single-phase source, where uniform torque is desired, as in the case of electric traction, to employ a phasechanger, which may be constructed hke an induction motor, and pol phase induction motors su plied from the phase-changer.

'The in uction motor is substantially a constant-speed machine, and when different s eeds are required it has been the practice either to vary the number of poles of the individual motor, or, in the case of a plurality of motors, to connect them in cascade and in parallel. uniform torque in operation from a singlephase source, and to employ the cascade method of control for varying s eeds, three machines are required with t e ordinary arrangement for obtaining two speeds, one

of the machines being employed as phasechanger, and the other two for the cascade and parallel connections. By my invention it is possible to obtain three speeds from such a combination. I accomplish this by roviding three induction motors, one wit a difierent number of poles from the other two, and so arranging the driving connections of the motors that either the first motor or one of the other two motors can be employed as phase-changer. Thus, for instance, if one motor is arranged with four poles and the other two with eight poles, then by employing the four-pole motor as phase-changer and connecting the other two machines in cascade, a speed. corresponding to sixteen poles is obtained; by using one of the eight-pole machines as phase-changer and connecting the other two machines in cascade a speed corresponding to twelve poles is obtained; and by connecting the ur pole machine as phase-changer and conmeet ng the other two machines in parallel as driving motors, a speed corresponding to If it is desired to obtain.

eight poles is obtained. For all three speeds a uniform tractive effort is obtained,

and two motors are employedat each speed for driving.

My invention, accordingly, in one aspect, consists in arranging two induction motors with different po e numbers and using them alternately asphase-changer and motor,

In anot er aspect my invention consists in providing two motors of different polenumers andmonnecting the third motor in catscade with either of the first two and directly to'the source.

My invention further consists in arranging the machine which is actin as phasechanger so that it gives a be anced poly phase voltage under load, as will be hereinafter explained.

My invention will best be understood by reference to theaccompanying drawings, in which Figure 1 shows a frame for a single-phase locomotive with its driving motors arranged in accordance with my invention; Fig. 2 shows a diagram of the motor circuits and controlling switches; Fig. 3 shows the starting connections for one of the motors; Fig.4 shows the running connections of the same; Figs. 5 and 6 are explanatory diagrams showing the method of obtaining balanced polyphase voltages under load; and Figs. 7, 8 and 9 are diagrams of the connections obtained in the three ositions of the speed-controlling switch in 2. I

In Fig. 1, i. represents the frame of a singleghase locomotive, and B B represent the riving wheels. The drivin wheels may be provided with connecting r0 s b b, so as to insure the same speed for all the wheels and to distribute the tractive e'liort equally amon the driving Wheels at all times. M, M and M represent the stators of three polyphase induction motors, which are sleeved on the driving axles, and are provided with ears or lugs engaging the frame of the machine, as-

means of which it may be connected to the is provided with a similar clutch C, while the rotor of the third motor M may be fast to the axle.

Referring now to Fig. 2, the stators and rotors of the several motors are indicated by the same reference letters as in Fig. 1, as are also the clutches C and O. D re resents the startin and reversing switch, the s eed contro ing switch, and F a switch w 'ch may be mechanically connected to the switch D, and by means of which balanced olyphase voltages are obtained under load or either direction of rotation. With the switch E in its first position indicated by 1 the primary circuits of motors M and M are 0 en. The clutches O and C are also open.

e primary winding of the motor M is connected through switch E to the starting and reversing switch D. Motor M is arranged for a different number of poles from motors M and M On the drawing, I have indicated that motor M is arranged for four poles, and the other two motors for eight poles. Consequently, for the first s eed motor M is to be operated as a phase-c anger, and motors M and M as driving motors in cascade. For starting in one direction or the other, switch D is moved toward the right or left, and switch F is similarly moved. Assume that switch D is moved toward the left into its first position; a circuit is then closed from the source of current, indicated by the trolley T, to contact (1 to contact (2 where the cur.- rent divides, part passing through the inductance I, contact (i contact (1 contact a, contact e, to terminal 1 of motor M ,-and the other part passing through resistance R, contact (2 contact (1, to terminal 8 of the motor The two terminals 1 and 8 of the motor are thus connected to the source through the phase-splitting device formed by the induct ance I and the non-inductive resistance R. The current entering the motor windin at terminal 1, passes out from termina 3 throu h contact f ,contact f to terminal 4. The p ases1-3 and 8-4 of the motor are consequently joined together at their inner terminals. Terminal 4 is also connected through contact e contact 'e, contact f contact to terminal 5 of the third phase of the motor; the other terminal 7 of this phase being connected to earth. The motor is thus connected in Y with one terminal to earth, and the other two terminals connected to the source through the phase-splitting device. A more or less uniform rotary field is thus produced in the stator winding M which causes the rotor m which is short-circuited through contacts e c and earth to come up to speed; the clutch circuit C being open at contact e, so that the rotor can start freely. After motor M is thus started and is running freely, starting switch D is moved to its secaccordingl be used as a phase-changer to supply po yphase voltages to the other two motors.

The starting and running connections of motor M which have been described above are indicated diagrammatically in Figs. 3 and 4 respectively. As indicated by the crossed-dotted lines in Fi 3, the motor M may be started in either direction, according as to which of terminals 1 and 8 is connecte to the resistance R, and which to the inductance I. It will be seen by tracing out the circuits in Fig. 2 that the only difference produced by moving switch D toward the right, instead of to the left as above described, is to reverse the relative connections of inductance I and resistance R to themotor terminals 1 and 8. It will be noted in passing that switch F produces no changes in circuit connections 1n moving from starting to running position.

Before describing the different connections established by switch E for the different speeds, the arrangement for obtaining balanced-polyphase voltages under load will be ex lained.

eferrin to Fig. 5, o-x, 0--] and oz represent the induced volta es at no-load in the primary windin of a p ase-changer for changin from singIe to threehase. The termina s y and z are suppose to be connected to the source. Such a machine, runnin free as a singlepha'se motor under noloa produces a near y uniform rotary field, so that the length of the line 0-:c is substantially the same as that of 0-"y and 0.z, the length of which is determined by the impressed voltage. The induced voltages at the terminals 11:, y and 2 would consequently be represented by an equilateral triangle,- or in other words, the phase-changer gives a balanced three-phase voltage under noload. As soon as the phase-changer is loaded, however, the conditions are changed. Assume that the current delivered from terminal a: is represented in phase and amount bythe line :r-w. This current produces a reactive and ohmic drop, the former of which may be represented by the line mv at rightangles to xw, while the ohmic dro is represented by the line H paralle to the line w-'w. The resultant drop is consequently 'mu, and the resultant terminal voltage of this phase is consequently'represented by o-a. The triangle 2 y a consequently represents the polyphase voltages III . and it will the phase-chan or under load,

supplied b.

be observed that t voltage ou is diminished in amount and distorted in angle.

base, so that the triangle is no longer equiateral, and the vclta es'are' no longer balance'd." This means 1: at the full output is not obtained from the motors supplied by the phase-changer, since the phases are not equally loaded.- In order to remedy this defect, I connect the phase-changer as shown diagrammatically in Fig. 6. In this figure one of the phases, the outer terminal 2 of which is connected to the source, has its inner terminal connected to an intermediate point -t on the phase For no-load, this connection gives unbalanced voltages re resented by the triangle a: 'y 2, but this un alanci at no-load is of no im' ortance. When the 1 ;:ase-chan 'er is loade with'a current delivered from die terminal at, represented by the line ac'w, a drop m-u is produced in the manner above ex lained, so that the phases of the induced vo ta es under load are represen-ted by the triang e u y 2.

It will be seen that this-is substantially an equilateral tri- That is, by properly'selecting the point of connection 't, approximately balso that the anced volt es under load may be obtained,

driving motors supplied from the phase-changer may deliver their full rated output. It will be seen that to obtain the above result the efiective turns between the terminals connected to' the source are less than between the third terminal and either of the first two, so that the voltage induced between the terminal not connected to the source and the other two terminals is greater .on no-load than the volta e of the source.

By thus arrangin the V0 tages of no-load the drop under fu -load is compensated for. It will further be noted that if a motor is connected as shown in Fig. 6, for one direction of rotation, the relative arrangement of a the two phases connected to the source should be reversed for the other direction of rotation. In other words, for the other direction of rotation the phase having its outer terminal connected to 2 should have its inner terminal connected to 0, while the phase having its outer terminal connected to 'yshould have its other terminal connected to an inter- With these urpose of leads F and mediate point on the first phase. points in mind, the

the different connections established thereby for the different positions of switch E will be clearly understood.

When switch Eis moved to its first running position, whichis indicated by 2*, the following connections are established. The connection from trolley T passing through switch D, as above explained, extends to contact e which is connected in the osition 2 to terminals -1 and 11 of motors i and M respectlvely, through contacts e and a. From terminal 1 the current passes out at intermediate terminal 2, through contacts f f, e, e, f and f, to terminal 5 and thencethrough phase 57 to earth. Phase 5-7 is thus connected to the intermediate terminal 2 of phase 13 in order to obtain heretofore exp ained. 13 is connected through contacts f 4 and f 5 the current passing in at terminal 111 asses out at terminal 13 throu h contacts, f and f", to terminal 14, w ich is connected through contacts e", e, f and f,-to terminal 15 of the third phase. Motor M which is to o erate as a driving motor in this position oFswitch E is thus connected in Y in the usual manner, the intermediate terminals 12 and 16 .both being open-circuited. Terminal 18 of motor M is connected through contacts e and e to terminal 8 of motor M so as to receive the voltage induced at this terminal in motor .M, which is running as a phase-changer, that is, motors M and M are connected in parallel with one phase connected to the source. Motor M is thus supplied with polyphase voltages and its rotor is connected mechanically to the driving wheels, since clutch C is energized through contacts a and e The rotorm is connected to the stator M? through contacts e and e, and through contacts 6" and e, and through earth, so that motors M and M? are connected in cascade. The motors consequently operate at a speed corresponding to sixteen poles. Thls connection is shown with the switch contacts omitted in Fig. 7. Now, if switch E is moved to its second runnin position, indicated at 3 the nect motor M to the driving motor, and at the same time rotor m is short-circuited for operation as phase-changer while rotor m is connected in cascade with the a stator M giving a speed corresponding to twelve poles. Furthermore, the stator of motor M is now connected in Y in the usual manner for operation as a motor, while the motor M is connee-ted in the special manner with terminal 15 connected to intermediate terminal 12, so

under loa as a phasechang'er. The above traced from Fig. 2 after the description that has been iven of the circuit connections formed in t e first running position of switch switch contactsomitted in Fig. 8. In the third running position of switch E indicated at 43 motor M is again connected as a phase changer, while the two eight-pole motors M and M are connected in parallel as driving motors. This connection will be evident from an inspection of the contact arrangebalanced poly hase voltages under load, as,

Terminal 3 of phase the circuit of clutch C is closed so as to eonas to sup ly balanced po'lyphase voltagesto terminal 4 of phase 48'. In motor M I mentioned circuit connections can be readily E. These connections are shown with the displaced toward the right, termin ment of Fig. 2 and from Fig.0, which shows the connections with the switch contacts omitted. Three speeds are thus obtained, corresponding to sixteen, twelve and eight oles respectively; two motors being used 1n each case as driving motors, and the third as a phase-changer. For operation in the reverse direction, switch E is returned to its offosition indicated at 1 and switches D an F are moved in the opposite direction from elf-position. The motor M is consecppcntly started in the opposite direction by t e reversal of its connection to the phasesplitting device formed by inductance I and resistance R. At the same time switch F makes the necessary changes in the circuit connections of motors M and M so that when switch-E is again moved to its operative positions the proper connections for hase-changer operation will be secured. hat is, with switch F in its other position, a 5 is no longer connected to terminal 2 when motor M acts as a phase-changer, but instead ter-' minal 3 is connected to terminal 6, and termi nal.5 instead of terminal 3 is now connected to terminal 4. The same changes are made with respect to motor M so that both motors are properly connected for operation both as driving motors and as phase-changers .for both directions of rotation.

I do not desire to limit myself to the particular construction and arrangement of parts here shown, but aim in the appended claims to cover all modifications which are within the scope of my invention.

What I claim as new and desire to secure by Letters'Patent of the United States, is:

1. In combination with a single-phase source, two polyphase induction motors of different polenumbers, a load to be driven thereby, means for connecting the primary windings of both motors in parallel, with one phase connected to the source,- and means for 1coniecting either motor mechanically to the 2. In combination with a single-phase.

source, two polyphase induction motors of different ole-numbers, a load to be driven, a switch a apted to connect the. rimary Windings of both motors in para el, wlth one phase connected to the source, and a magnetic clutch for each motor adapted to connect it mechanically to the load.

3. In combination with a single phase source, two polyphase induction motors of mechanically to the load, and means for dis+ connecting the rotor of the second motor from the load and connecting the rotor of the first motor thereto.

4. In combination with a source of alternating current, two induction motors of different pole-numbers, a third induction motor,

and means for connecting the third motor in of the same pole-number.

6. In combination witha singlephase source, two polyphase induction motors of different pole-numbers, a load to be driven thereby, means for connecting the primary windings of both motors in parallel, with one phase connected to the source, means for connecting either motor mechanically to the load, a third motor mechanically connected to the load, and means for connecting it in cascade with either of the first two motors.

7. In combination with a singlephase source, two polyphase induction motors of difi'erent pole-numbers, a load to be driven thereby, means for connecting the primary windings of both motors in parallel, with one phase connected to the source, means for connecting either motor mechanically to the load, a third motor mechanically connected to the load having the same number of poles as one of the first two motors, and means for electrically connecting it in cascade with either of the first two motors and in arallel with the motor of the same pole-num er.

8. In combination with a sin le-phase supply circuit and a polyphase loa circuit, a phase-changer consisting of a polyphase induction motor having its primary connected to both circuits and arran ed todeliver under load substantially ba lanced polyphase voltages to the load circuit.

9. A phase-changer for converting singlephase into polyphase currents consisting of a polyphase induction motor having its primary winding connected and arrangpd to deliver substantially balanced polyp ase voltages under load.

10. A phase-changer for converting singlephase into polyphase currents consisting of a. poly hase mduction motor having a number of e ective turns in the phase of its primary winding connected across the sing e-phase source smaller than the number ofeflective turns in another phase.

11. A phase-changer for converting singlephase into pol phase currents consisting of a polyphase in uctionmotor having its primary winding connected and arranged to produce an induced electromotive force in the phase connected to the singlehase source smaller on no-load than the e ectromotive force induced in another phase.

12. A phase-changer for converting singlephase into three-phase currents consisting of a three-phase induction motor having its primary winding connected in Y but with the inner terminal of one phase connected to an intermediate point on one of the other two phases.

13. A single-phase locomotive comprising two poly hase induction motors of different pole-num ers, means for connecting both motors in parallel with one base connected to the source of current, and means for connecting either motor mechanically to the driving Wheels.

14. An electric locomotive comprisin two induction motors of different pole-num ers,

a third induction motor having the same.

number of poles as one of the first two, and means for connecting the third motor in cascade with either of the other two and in parallel with the one having the same polenumbers.

15. A single-phase locomotive comprising two poly hase induction motors of difierent pole-num ers, means for connecting both motors in parallel with one phase connected to the source of current, means for connecting either wheels, a third motor mechanically connected to the driving wheels, and means for connecting it in cascade with either of the other two motors.

16. The method of driving a load at different speeds from a single-phase source by means of polyphase inductlon motors of different pole-numbers, which consists in connecting the primary windings of the motors in parallel with one phase connected to the source and mechanically connecting the rotors of the motors alternately to the load.

17. The method of driving a load at dilierent speeds from a single-phase source by means of polyphase motors of different polenumbcrs, which consists in o crating each motor alternately as a phase-c ranger and as a driving motor for the load.

18. The method of driving a load at difi'ermotor mechanically to the drivingent speeds from a single-phase source b means of polyphase induction motors ofdi ferent pole-numbers which consists in operating each motor alternately, running free as a phase-changer and wit its rotor mechanically connected to the load as a driving motor therefor.

19. The method of obtaining three driving speeds from three induction motors, two of which have different pole-numbers, which consists in connecting t e third motor in cascade with either of the other two to the source.

20. The method of obtaining three driving speeds from three induction motors, of which two have difierent pole-numbers and the third has the same number of poles as one of the first two, the third rotor in cascade with either of the other two and in parallel with the other motor of the same pole-number.

21. The method of operating a singleand directly induction motors of di erent pole-numbers, which consists in running one motor free as a phase-changer supplying polyphase current to a second motor, and clutching the second motor'to the driving wheels, and then running the second motor free as a phasechanger and clutching the first motor to the driving wheels.

22. The method of operating a singlehase locomotive equi ed with poly hase induction motors, of w ch two have 'fierent pole-numbers and the third has the same number of poles as one of the first two, which consists in connecting the third motor alternately in cascade with each of the first two motors and in parallel with the one having the same ole-number and using the motor not emp oyed in making each of the three connections as a phase-changer for sup plying polyphase currents to the other two motors that are connected in cascade or in parallel.

In witness whereof, I have hereunto set my hand this 7th day of July, 1906.

ERNST F. W. ALEXANDERSON.

Witnesses:

BENJAMIN B. HULL, HELEN ORFORD.

phase locomotive equi ped with polyphase which consists in connecting 

